You don’t need to know either her music or her style to be familiar with Lily Allen. And even if, like me, you aren’t that interested in the hit singles or the range of looky-likey clothes, she probably scores several points on your personal respectometer for the simple achievement of being herself when all around her are busy conforming to the pop-dolly ideal. In these strangely conformist times, Allen has become a beacon of independence, a shining example of what happens when a girl says: “Hello, world. This is me. I am happy without the makeover. See, I’m even successful.” She may have started out as a singer, but she has become the poster girl for young women everywhere who want to be allowed to have puppy fat, wear dizzy clothes that aren’t necessarily “fashion”, let their mascara run and generally enjoy the thrill and power and endless contradictions of being young and female in the 21st century.

Which is why a blog entry recently posted on Allen’s MySpace page rocked more than her core fanbase. Headlined: “Fat, ugly and shitter than Winehouse” (a reference to the bad blood between her and Amy Winehouse), it continued: “I used to pride myself on being strong-minded and not being some stupid girl obsessed with the way I look. I felt like it didn’t matter if I was a bit chubby ’cause I’m not a model, I’m a singer. I’m afraid I am not strong and have fallen victim to the evil machine.” Holed up in a Seattle hotel, Allen had apparently succumbed, like so many before her, not to the pressures of touring, promoting and recording – that’s all manageable – but to body-image insecurity. Everyone carries it, but, as with MRSA, you just need the right cocktail of neglect and lowered resistance for it to flourish – a lonely tour in a foreign land will do nicely.

Poor Allen. Having launched a range of clothes for New Look and having been endlessly quoted on the subject of wanting ordinary girls to feel good about themselves in wearable kit, as opposed to Kate Moss microshorts, she wrote: “I have spent the last hour researching gastric bypass surgery and laser liposuction.” Ouch. Even if it was just a wobble (and, sure enough, she took it back a day or so later), this was still a significant blow to the “free young women from image oppression” cause. We look to Allen for normal-girl leadership, normal experimenting with clothes, normal bad hair decisions, bad-skin days and bad eating habits, in the way women over 40 look to Geena Davis and Helen Fielding for late-fertility inspiration. And it matters because there aren’t a lot of role models out there.

Maybe it was the isolation that temporarily pushed Allen over the edge. If you look around, she is, incredibly, in a club of one. Every other female singer or actress you care to mention, bar Beth Ditto, is model-sized (and if they have the hair, the breasts and the overstyled look, so much the better). A few years ago, there was Sophie Dahl, but then she got with the programme. There was Winehouse – famously nonconformist and determined to live by her rules – but she caved in, lost half her body weight and then declared her former self “big”. Even the rebel artist is not immune to the tyranny of downsizing.

Before Allen hit the big time (or, as it should be known, the thin time), she will have looked in the mirror and thought, “La, la, la,” at least some of the time. Now, she has become public property; with that comes media scrutiny and comparing yourself to other females in a similar situation – specifically Moss – and, bingo, so it begins: tweaking that inch of midriff fat; plucking at the pad of flesh in the cleft of your armpit; spinning around to look at your bum in the mirror again and again, until you can’t remember who you are, what you have achieved, how much you are loved or how many people have quite fancied you despite all your terrible imperfections.

But being in the spotlight is only part of the problem. The reason Allen’s blog revelation had a ripple effect way beyond MySpace browsers is because feeling fat and ugly is a state of mind that all women are familiar with, not just the much-photographed ones. You don’t have to be fat or ugly to go there, as Allen has demonstrated; you just have to be female and down, which means down on yourself and, in particular, your appearance. When men get low, they worry about how much they have achieved, whether or not they have sold themselves short, whether they should be leaving their jobs. Women – regardless of their physical qualities – go straight to fat and ugly and, however much evidence there is to the contrary, commence beating themselves into a not-good-enough pulp. Jane Fonda, Elle Macpherson, Jennifer Aniston – they are all women who, in their time, have felt bad about the way they look. If Fonda filming Barbarella thought of herself as a bit of a dog, you get the scale of the problem, not to mention a bit of historical perspective. Youth, good looks, success and money are no defence against the female mind’s capacity for self-sabotage.

Allen has since recovered her poise and explained that she was under pressure from all the Kate-Lily picture comparisons in the press, which made her feel momentarily “grotesque”. She adds: “I guess it shows how much of an effect the media can have on us young ladies.” Well, yes. But, in or out of the limelight, with or without the current obsession with size, we women will always turn straightforward tiredness or PMT or an everyday work crisis or a boring weekend into a fat and ugly downward spiral, and it’s that we have to work on as much as banning models who live on grapefruit.

How we go about it is debatable, though there are three factors that undoubtedly help. Having a loving, attentive father (the root of a girl’s self-esteem). Having a loving, attentive partner, who doesn’t secretly hanker after your opposite physical type. And getting a few years into your forties – after which you have to deal with losing what looks and figure you ever had, but (good news) the fat-and-ugly default mode turns into straightforward grumpy (so much easier).

Small comfort, but it is something for Allen to hold on to when she is next considering plastic surgery.

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